Dry method for preparation of inulin biomass as a feedstock for ethanol fermentation

Abstract

Sisal leaves which constitute only 2% of the sisal plant have been used in the production of pulp and fiber; the remaining 98% which is mostly of the sisal bole is largely regarded as waste. The bole’s high inulin fraction (24-
36%) is of particular significance due to its chemical functionality and relative ease of fermentation. utilisationThe objective of this study was to identify properties and pertinent characteristics for developing industrially viable methods of extracting inulin from sisal bole in a readily utilisable form. Inulin was extracted using the dry method ‘baking’, whereby sisal boles were chopped into chips of defined sizes 1.5-6 cm, before drying at 70 - 150 °C. The dried bole chips were milled to sieved powder of 90-2000 ìm. Particle sizes and temperature for total sugars were determined using the dinitrosalicylic (DNS) colorimetric method. Prior to fermentation, the inulin was hydrolysed using sulphuric acid to give a total sugar yield of 5-16% wt/wt depending on drying temperature. In general, high temperatures, e.g. 150 oC led to low sugar recovery (10.3% wt/wt), while low temperatures, e.g. 70 oC gave high sugar recovery (16.3% wt/wt). The fine inulin powder (<250 ìm) was richer sugar content (~16%), whereas coarse particles (>400 ìm) gave low sugar levels (~9%). The hydrolysed inulin was fermented using Saccharomyces cerevisiae for 57 hours giving consistent ethanol yields depending on initial sugar levels.